Lukas Brander1, Onnen Moerer2, Göran Hedenstierna3, Jennifer Beck4, Jukka Takala5, Arthur S Slutsky6, Christer Sinderby7. 1. Interdepartmental Division of Critical Care Medicine, University of Toronto, Department of Critical Care Medicine, St. Michael's Hospital, Toronto, Canada; Department of Intensive Care Medicine, Cantonal Hospital of Lucerne, Switzerland. Electronic address: lukas.brander@luks.ch. 2. Interdepartmental Division of Critical Care Medicine, University of Toronto, Department of Critical Care Medicine, St. Michael's Hospital, Toronto, Canada; Department of Anaesthesiology, Emergency and Critical Care Medicine, University of Göttingen, Germany. 3. Department of Medical Sciences, Clinical Physiology, University of Uppsala, Uppsala, Sweden. 4. Department of Pediatrics, University of Toronto, Toronto, Canada; Keenan Research Centre for Biomedical Science and Li Ka Shing Knowledge Institute of St. Michael's Hospital, Toronto, Canada; Institute for Biomedical Engineering and Science Technology (iBEST) at Ryerson University and St. Michael's Hospital, Toronto, Canada. 5. Department of Intensive Care Medicine, Bern University Hospital - Inselspital, and University of Bern, Switzerland. 6. Interdepartmental Division of Critical Care Medicine, University of Toronto, Department of Critical Care Medicine, St. Michael's Hospital, Toronto, Canada; Keenan Research Centre for Biomedical Science and Li Ka Shing Knowledge Institute of St. Michael's Hospital, Toronto, Canada. 7. Interdepartmental Division of Critical Care Medicine, University of Toronto, Department of Critical Care Medicine, St. Michael's Hospital, Toronto, Canada; Keenan Research Centre for Biomedical Science and Li Ka Shing Knowledge Institute of St. Michael's Hospital, Toronto, Canada; Institute for Biomedical Engineering and Science Technology (iBEST) at Ryerson University and St. Michael's Hospital, Toronto, Canada.
Abstract
BACKGROUND: Endogenous pulmonary reflexes may protect the lungs during mechanical ventilation. We aimed to assess integration of continuous neurally adjusted ventilatory assist (cNAVA), delivering assist in proportion to diaphragm's electrical activity during inspiration and expiration, and Hering-Breuer inflation and deflation reflexes on lung recruitment, distension, and aeration before and after acute lung injury (ALI). METHODS: In 7 anesthetised rabbits with bilateral pneumothoraces, we identified adequate cNAVA level (cNAVAAL) at the plateau in peak ventilator pressure during titration procedures before (healthy lungs with endotracheal tube, [HLETT]) and after ALI (endotracheal tube [ALIETT] and during non-invasive ventilation [ALINIV]). Following titration, cNAVAAL was maintained for 5min. In 2 rabbits, procedures were repeated after vagotomy (ALIETT+VAG). In 3 rabbits delivery of assist was temporarily modulated to provide assist on inspiration only. Computed tomography was performed before intubation, before ALI, during cNAVA titration, and after maintenance at cNAVAAL. RESULTS: During ALIETT and ALINIV, normally aerated lung-regions doubled and poorly aerated lung-regions decreased to less than a third (p<0.05) compared to HLETT; no over-distension was observed. Tidal volumes were<5ml/kg throughout. Removing assist during expiration resulted in lung de-recruitment during ALIETT, but not during ALINIV. During ALIETT+VAG the expiratory portion of EAdi disappeared, resulting in cyclic lung collapse and recruitment. CONCLUSIONS: When using cNAVA in ALI, vagally mediated reflexes regulated lung recruitment preventing both lung over-distension and atelectasis. During non-invasive cNAVA the upper airway muscles play a role in preventing atelectasis. Future studies should be performed to compare these findings with conventional lung-protective approaches.
BACKGROUND: Endogenous pulmonary reflexes may protect the lungs during mechanical ventilation. We aimed to assess integration of continuous neurally adjusted ventilatory assist (cNAVA), delivering assist in proportion to diaphragm's electrical activity during inspiration and expiration, and Hering-Breuer inflation and deflation reflexes on lung recruitment, distension, and aeration before and after acute lung injury (ALI). METHODS: In 7 anesthetised rabbits with bilateral pneumothoraces, we identified adequate cNAVA level (cNAVAAL) at the plateau in peak ventilator pressure during titration procedures before (healthy lungs with endotracheal tube, [HLETT]) and after ALI (endotracheal tube [ALIETT] and during non-invasive ventilation [ALINIV]). Following titration, cNAVAAL was maintained for 5min. In 2 rabbits, procedures were repeated after vagotomy (ALIETT+VAG). In 3 rabbits delivery of assist was temporarily modulated to provide assist on inspiration only. Computed tomography was performed before intubation, before ALI, during cNAVA titration, and after maintenance at cNAVAAL. RESULTS: During ALIETT and ALINIV, normally aerated lung-regions doubled and poorly aerated lung-regions decreased to less than a third (p<0.05) compared to HLETT; no over-distension was observed. Tidal volumes were<5ml/kg throughout. Removing assist during expiration resulted in lung de-recruitment during ALIETT, but not during ALINIV. During ALIETT+VAG the expiratory portion of EAdi disappeared, resulting in cyclic lung collapse and recruitment. CONCLUSIONS: When using cNAVA in ALI, vagally mediated reflexes regulated lung recruitment preventing both lung over-distension and atelectasis. During non-invasive cNAVA the upper airway muscles play a role in preventing atelectasis. Future studies should be performed to compare these findings with conventional lung-protective approaches.